With sub-micron semiconductor manufacturing process being the prevalent technology, the demand for a high-resolution photolithographic process has increased. The resolution of a conventional photolithographic method is primarily dependent upon the wavelength of a light source, which dictates that there be a certain fixed distance between patterns on a photoresist. Distance separating patterns smaller than the wavelength of the light source could not be accurately patterned and defined.
Prior art light sources with lower wavelengths are normally used in a high-resolution photolithographic process. In addition, the depth of focus of a high-resolution photolithographic process is shallower compared to a relative low-resolution photolithographic process. As a result, a photoresist layer having a lower thickness is required for conventional photolithographic methods. However, a photoresist layer having a lower thickness is susceptible to the subsequent etching steps in a semiconductor manufacturing process. This relative ineffective resistance to etching reduces the precision of patterning and defining of a photoresist. These limitations prevent the dimensions of patterns on a photoresist from being reduced.
It is accordingly a primary object of the invention to provide a method for reducing the distance separating patterns on a photoresist layer. In addition, it is another object of the invention to provide a method to enhance the etching resistance of a patterned photoresist layer.